New Green OLED Lights Could be Printed on Plastic

An Israeli is part of a team to invent a new kind of “green” LED light called the OLED. If brought from theory to practice they could be manufactured from plastics and made by ink jets.

Valy Vardeny and Tho D. Nguyen from the University of Utah (Salt Lake City) worked with Eitan Ehrenfreund from Technion-Israel Institute of Technology (Haifa) to invent spintronic organic light-emitting diodes (OLEDs). A paper describing their invention was published in the journal Nature. Vardeny said spintronic OLEDs could lead to a cheaper, brighter and greener light source.

Greenprophet has written about the unsustainable use of endangered words such as sustainable so we should thank these scientists not only for their amazing technology but also for introducing some fresh and wonderfully fun words into our green vocabulary. Let’s have a look at our new words:

Bipolar Organic Spin Valve: A version of the above which can generate light by sending electrons in on one electrode and holes in on the other. One nice advantage of sprintronic bipolar organic spin valve organic LEDs is that the wavelength can be controlled by applying an external magnetic field.

The cobalt electrodes were also treated with Lithium Fluoride, perhaps because this device is bipolar. The device currently produces a dim orange light and must be refrigerated to at least -28 degrees Fahrenheit (-33 degrees Celsius.) But it does show promise. Even if the invention is never practical, at least we got to use those fun words!

Excitons: I’m not making this up folks, you’ve heard of photons, neutrons, protons, electrons and bosons but now we have excitons. Who knew? Excitons are created when electrons and holes (places in a crystal where there aren’t electrons) combine.

Ordinary LEDs work by pushing electrons so that they fall into ‘holes’ (spaces where there aren’t electrons) inside a semiconductor crystal. The energy released by this recombination is called an exciton and it emits light with an energy proportional to the distance (bandgap voltage) of the fall. Since energy and wavelength are related, high energy falls produce blue light, lower energy falls produce red light.

Organic Light Emitting Diodes (OLEDs): Unlike organic cucumbers and free-range chickens, OLEDs can be less expensive and less time consuming than their inorganic cousins. This is because ordinary LEDs must be grown as crystals of expensive and very pure materials with carefully measured impurities. OLEDs are based on plastics and they can be painted or even ink-jet printed onto a surface.

Spintronics: Why haven’t we seen this word before? Surely there must have been an awesome 1970s disco-ball band with this name. I need to check my 8-track collection but Google tells me that spintronics is like electronics except that instead of manipulating the flow of electrons and storing data as an electron charge on a RAM bit, we can now toggle an electron’s spin between ‘up’ and ‘down’. The invention which makes this possible is called an organic spin valve.

Organic Spin Valve: Was also invented by Vardeny’s team and published in Nature in 2004. Utah news explains it in friendly terms:

“Organic spin valves are comprised of three layers: an organic layer that acts as a semiconductor and is sandwiched between two metal electrodes that are ferromagnets. In the new spin OLED, one of the ferromagnet metal electrodes is made of cobalt and the other one is made of a compound called lanthanum strontium manganese oxide. The organic layer in the new OLED is a polymer known as deuterated-DOO-PPV, which is a semiconductor that emits orange-colored light.”

So there you go. But kids, even if mom happens to have heavy hydrogen, ferromagnetic cobalt and gold-plated lanthanum strontium manganese oxide in her kitchen, you really shouldn’t try to make spintronic OLEDs at home. It could be much more dangerous than eating raw cookie dough.